Environmental sustainability analysis of dairy bedding regeneration system based on emergy evaluation and life cycle assessment methods.

Dairy farm bedding can be produced by composting technology using dairy manure, which offers advantages in terms of cost, availability, and economic value. However, few information is available on the environmental sustainability and impacts for manure recycling systems based on different composting methods. The resource-environmental impact and eco-economic sustainability of two manure bedding regeneration systems: forced-ventilation static-stack aerobic fermentation (FVSSAF) system (Scenario A) and bedding recovery unit (BRU) system (Scenario B) were evaluated in this study. The life cycle assessment yielded a combined environmental impact potential of 0.01032 for scenario B, much lower than the 0.02656 for scenario A. The emergy evaluation showed that scenario B can handle more dairy manure than scenario A due to 57% increase of emergy input. Form the emergy indices of the two systems, scenario B had lighter environmental pressure and higher sustainability. Therefore, the BRU system had economic advantages and ecological sustainability, which was more suitable for large dairy farms. The trade-offs between environmental consequences, resource efficiency, and economic benefits were analyzed from several perspectives in this study, which would help stakeholders to have a new understanding when choosing a bedding recycling system.

Highly stable selenium nanoparticles: Assembly and stabilization via flagellin FliC and porin OmpF in Rahnella aquatilis HX2.

Microorganisms play a critical role in the reduction of the more toxic selenite and selenate to the less toxic elemental selenium. However, the assembly process and stability of selenium nanoparticles (SeNPs) remain understudied. The plant growth-promoting rhizobacterium Rahnella aquatilis HX2 can reduce selenite to biogenic SeNPs (BioSeNPs). Two main proteins, namely flagellin FliC and porin OmpF were identified in the BioSeNPs. The fliC and ompF gene mutation experiments demonstrated that the FliC and OmpF could control the assembly of BioSeNPs in vivo. At the same time, the expressed and purified FliC and OmpF could control the assembly of SeNPs in vitro. BioSeNPs produced by R. aquatilis HX2 exhibited high stability under various ionic strengths, while the chemically synthesized SeNPs (CheSeNPs) showed a high level of aggregation. The in vitro experiments verified that FliC and OmpF could prevent the aggregation of the CheSeNPs under various ionic strengths. This work reports the preparation of highly stable BioSeNPs produced by strain R. aquatilis HX2 and verifies that FliC and OmpF both could control the assembly and stability of BioSeNPs. BioSeNPs with high stability could be suitable as nutritional supplement to remedy selenium deficiency and in nanomedicine applications.

Selenium Biofortification and Antioxidant Activity in Cordyceps militaris Supplied with Selenate, Selenite, or Selenomethionine.

Selenium (Se) is an essential trace element with multiple functions that may help mitigate adverse health conditions. Cordyceps militaris is an edible mushroom with medicinal properties. The experiment was conducted under artificial cultivation, with five Se concentrations (0, 5, 10, 20, and 40 µg g-1) and three forms of Se (selenate, selenite, and selenomethionine). C. militaris can absorb inorganic from the substrate and convert it to organic Se compounds (selenocystine, selenomethionine, and an unknown species) in fruiting bodies. Compared with the control treatment, Se applications (40 µg g-1 selenate and selenite) significantly increased the Se concentration in fruiting bodies by 130.9 and 128.1 µg g-1, respectively. The biofortification with selenate and selenite did not affect fruiting body production, in some case, but did enhance the biological efficiency. Moreover, the abundance of cordycepin and adenosine increased, while the amino acid contents remained relatively stable. Meanwhile, Se-biofortified C. militaris showed effective antioxidant activities. These results suggest that Se-biofortified C. militaris fruiting bodies may enhance human and animal health when it was included as part of a healthy diet or used as Se supplements.

Absorption and Bio-Transformation of Selenium Nanoparticles by Wheat Seedlings (Triticum aestivum L.).

Elemental selenium is one of the dominant selenium species in soil, but the mechanism of its uptake by plants is still unclear. In this study, nanoparticles of elemental selenium (SeNPs) with different sizes were prepared, and their uptake and transformation in wheat (Triticum aestivum L.) were analyzed in hydroponic experiments by HPLC-ICP-MS. We found that the SeNPs can be absorbed by wheat seedlings, and the process is energy independent. The addition of aquaporins inhibitor caused 92.5 and 93.4% inhibition of chemosynthesized SeNPs (CheSeNPs) and biosynthesized SeNPs (BioSeNPs) absorption by wheat roots, respectively. The 40 nm SeNPs uptake by wheat roots was 1.8-fold and 2.2-fold higher than that of 140 and 240 nm, respectively. The rate of SeNPs uptake in wheat was much slower than that of selenite [Se (IV)], and CheSeNPs were more efficiently absorbed than BioSeNPs. The SeNPs were rapidly oxidized to Se (IV) and converted to organic forms [selenocystine (SeCys2), se-methyl-selenocysteine (MeSeCys), and selenomethionine (SeMet)] after they were absorbed by wheat roots. Additionally, we demonstrated that the aquaporin function in some way is related to the absorption of SeNPs. The particle size and synthesis method of the SeNPs affected their uptake rates by plants. Taken together, our results provide a deep understanding of the SeNPs uptake mechanism in plants.

Biosynthesis of selenium nanoparticles and effects of selenite, selenate, and selenomethionine on cell growth and morphology in Rahnella aquatilis HX2.

Rahnella aquatilis HX2 (proteobacteria) shows tolerance to selenium (Se). The minimum inhibitory concentrations of selenomethionine (Se-Met), selenite [Se (IV)], and selenate [Se (VI)] to HX2 are 4.0, 85.0, and 590.0 mM, respectively. HX2 shows the ability to reduce Se (IV) and Se (VI) to elemental Se nanoparticles (SeNPs). The maximum production of SeNPs by HX2 strain is 1.99 and 3.85 mM in Luria-Bertani (LB) broth with 5 mM Se (IV) and 10 mM Se (VI), respectively. The morphology of SeNPs and cells were observed by transmission electron microscope, environmental scanning electron microscope, and selected area electric diffraction detector. Spherical SeNPs with amorphous structure were found in the cytoplasm, membrane, and exterior of cells. Morphological variations of the cell membrane were further confirmed by the release of cellular materials absorbed at 260 nm. Flagella were inhibited and cell sizes were 1.8-, 1.6-, and 1.2-fold increases with the Se-Met, Se (VI), and Se (IV) treatments, respectively. The real-time quantitative PCR analysis indicated that some of the genes controlling Se metabolism or cell morphology, including cysA, cysP, rodA, ZntA, and ada, were significantly upregulated, while grxA, fliO, flgE, and fliC genes were significantly downregulated in those Se treatments. This study provided novel valuable information concerning the cell morphology along with biological synthesis process of SeNPs in R. aquatilis and demonstrated that the strain HX2 could be applied in both biosynthesis of SeNPs and in management of environmental Se pollution.